In general, the hydraulic excavator as a representative example of the construction machine comprising: an automotive vehicle body; an engine that is mounted on the vehicle body; an exhaust gas purifying device that is connected to an exhaust pipe of the engine and is provided with a urea selective reduction catalyst that removes a nitrogen oxide in an exhaust gas; a urea water injection valve that is provided in the exhaust gas purifying device and injects urea water that is a reducing agent to the upstream side of the urea selective reduction catalyst; a urea water tank that stores the urea water to be supplied to the urea water injection valve; a urea water pump that supplies the urea water that is stored in the urea water tank toward the urea water injection valve.
In this case, the urea water tank and the urea water pump are connected to each other via a suction pipeline through which the urea water that is sucked from the urea water tank toward the urea water pump flows and a return pipeline through which the urea water that is returned from the urea water pump toward the urea water tank flows. The urea water pump and the urea water injection valve are connected to each other via a supply pipeline through which the urea water that is supplied toward the urea water injection valve by the urea water pump flows.
A warming pipeline through which engine cooling water warmed by an engine flows is provided in the urea water tank and suppresses (defrosts) freezing of the urea water stored in the urea water tank (Patent Document 1). In addition, the one that uses the engine cooling water warmed by the engine and the one that uses a heater such as a heating wire and the like are known as the ones that suppress freezing of the urea water in the suction pipeline, the return pipeline, the supply pipeline.